#0289

Longest Consecutive Sequence

MediumDSA28 min20 XP

Problem

Given nums, return the length of the longest consecutive sequence. The sequence values must increase by 1, but they do not need to be adjacent in the original list.

Why This Matters

This problem tests whether you can use a set to start work only at sequence beginnings instead of sorting.

Function Signature

def longest_consecutive(nums):

Examples

Example 1

Inputnums = [100,4,200,1,3,2]

Output4

The longest run is 1, 2, 3, 4.

Constraints

Return the exact requested value.
Handle edge cases cleanly.
Use the intended DSA pattern when brute force would scale poorly.

CodePython

def longest_consecutive(nums):
    """
    Input example: nums = [100,4,200,1,3,2]
    Return: 4
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

def longest_consecutive(nums):
    """
    Input example: nums = [100,4,200,1,3,2]
    Return: 4
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Classic unsorted run

Input[100,4,200,1,3,2]

Expected4

The values 1 through 4 form the longest sequence.

Duplicates included

Input[0,3,7,2,5,8,4,6,0,1]

Expected9

Duplicates do not break the 0 through 8 run.

Hidden Test Categories

empty inputnegative numbersall duplicates